Effect of rolling process on microstructure and mechanical properties of Q&P steel

doi:10.13251/j.issn.0254-6051.2025.04.026

Abstract

Abstract: Hot-rolled and cold-rolled C-Si-Mn sheets with the same composition and thickness were subjected to intercritical austenitization, followed by direct water quenching and quenching and partitioning (Q&P) treatment, respectively. The microstructure and mechanical properties of direct water quenched and Q&P treated sheets were investigated by means of SEM, EBSD, TEM, tensile testing machines. The results show that the microstructure of the directly water quenched sheets mainly consists of ferrite and martensite. The microstructure the cold-rolled sheets after direct water quenching is mainly blocky and the hot-rolled sheets is mainly lath-like. After Q&P treatment, the retained austenite content of the sheets significantly increases, and the main morphology of retained austenite in the cold-rolled Q&P steel and hot-rolled Q&P steel are blocky and lathy, respectively. The volume fraction and carbon content of retained austenite in the hot-rolled sheet after Q&P treatment are higher and smaller in size compared to the cold-rolled sheet. The sheets after Q&P treatment exhibit lower strength but significantly higher ductility and product of strength and elongation (PSE) compared to the direct water quenched sheets, and the hot-rolled Q&P sheet shows better ductility and PSE than the cold-rolled Q&P sheet. The excellent plasticity of the hot-rolled sheet after Q&P treatment is mainly attributed to the higher content and the higher mechanical stability of retained austenite, which significantly extends the TRIP effect region. Therefore, compared with the direct water quenching, the Q&P treatment can significantly improve the elongation and PSE of the steel, and using hot-rolled sheet with initial microstructure of martensite+ferrite for Q&P treatment can obtain better PSE than the cold-rolled sheet with initial microstructure of pearlite+ferrite.

Key words: rolling process, Q&P steel, content of retained austenite, stability of retained austenite, strength and plasticity

CLC Number:

TG142.1

Zhang Menglan, Xu Deming, Zhang Dingkun, Deng Qiuyang, Fang Linhua, You Shiqi, Deng Siyang. Effect of rolling process on microstructure and mechanical properties of Q&P steel[J]. Heat Treatment of Metals, 2025, 50(4): 180-187.

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